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Post subject: 1965 blackface aa165
Posted: Thu Dec 25, 2014 1:36 pm
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i'm enclosing pics of my bassman. please note that it appears to be an aa165 but i'm not sure. some of the caps have been replaced and i'll recap the 20uf caps as the amp is rather noisy.

any further replace or repair situations that i might do? i'm not sure about the hum balance pot as to how to use it. perhaps that would get rid of the hum but i'll do the caps first.

serial on chassis is A08153

thanks,
mikeB.
Image

Image

Image

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Last edited by MikeB on Thu Dec 25, 2014 1:44 pm, edited 1 time in total.

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Post subject: Re: 1965 blackface aa165 pt. 2
Posted: Thu Dec 25, 2014 1:40 pm
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i didn't know the forum would only allow 3 photos, so here are a couple more.

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Post subject: Re: 1965 blackface aa165
Posted: Thu Dec 25, 2014 1:51 pm
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I do not see hum balance pot on your amp chassis photo .

AA165 do not use hum balance pot .

What kind of noise ?
Defective filters caps = hum

White noise , sshh = mostly 12XX7 plates resistors .

The new blue bypass caps are low quality caps , best is to use Sprague Atoms ,not expensive and they are the best replacement for this good amp .

https://www.tubesandmore.com/products/C-SA

Some of filter caps are low quality too.

For filter caps , use F & T caps

https://www.tubesandmore.com/products/C-ET22-500-FT

Replace the bias caps , close to pilot lamp, for a 100 MFD / 100 volts


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Post subject: Re: 1965 blackface aa165
Posted: Thu Dec 25, 2014 2:02 pm
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To resume ;

Replace;

1- All blue new cheap bypass caps and the old one , 2 in 1 brown ,at far right

2- All filter caps , include the news cheap one and the bias cap too

3- 12XX7 plates resistor if white noise

With good quality caps you'll have a great sounding amp for long time .

Check carefully polarity on Bias caps it is not standard and for some filter caps in dog house , some are reverse


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Post subject: Re: 1965 blackface aa165
Posted: Thu Dec 25, 2014 2:16 pm
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transformer XXX-502 = 1965 , second week of the year.

XXX-512 = 1965 , 12 week .....

Bias pot look a wiring like a balance pot as AB165 use , not like AA165 use.

I do not say it is a AB165 amp , not sure for now

A better close up will help

AB165 layout and schematic ;

http://el34world.com/charts/Schematics/ ... _schem.pdf


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Post subject: Re: 1965 blackface aa165
Posted: Thu Dec 25, 2014 3:45 pm
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stratele52 wrote:
transformer XXX-502 = 1965 , second week of the year.

XXX-512 = 1965 , 12 week .....

Bias pot look a wiring like a balance pot as AB165 use , not like AA165 use.

thanks for the info. so that is a bias pot and not the hum balance pot? guess i'd better get a bias probe if that is the case. any recommendations for the bias probe setup? also, i usually do use the F&T thru amplified parts/antique electronics.
thanks again,
mikeB

I do not say it is a AB165 amp , not sure for now

A better close up will help

AB165 layout and schematic ;

http://el34world.com/charts/Schematics/ ... _schem.pdf

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Post subject: Re: 1965 blackface aa165
Posted: Thu Dec 25, 2014 3:49 pm
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stratele52 wrote:
I do not see hum balance pot on your amp chassis photo .

AA165 do not use hum balance pot .

What kind of noise ?
Defective filters caps = hum

White noise , sshh = mostly 12XX7 plates resistors .

The new blue bypass caps are low quality caps , best is to use Sprague Atoms ,not expensive and they are the best replacement for this good amp .

https://www.tubesandmore.com/products/C-SA

Some of filter caps are low quality too.

For filter caps , use F & T caps

https://www.tubesandmore.com/products/C-ET22-500-FT

Replace the bias caps , close to pilot lamp, for a 100 MFD / 100 volts


+1

Mike,

Welcome to the forum.

The only thing I would add to stratele52's already excellent advice would be to replace the power cord with a 3 prong variety and get rid of the "death cap".

Thanks for posting pictures, it makes a huge difference as far as offering advice.

Merry Christmas!
vinyl


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Post subject: Re: 1965 blackface aa165
Posted: Thu Dec 25, 2014 3:52 pm
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vinyl wrote:
stratele52 wrote:
I do not see hum balance pot on your amp chassis photo .

AA165 do not use hum balance pot .

What kind of noise ?
Defective filters caps = hum

White noise , sshh = mostly 12XX7 plates resistors .

The new blue bypass caps are low quality caps , best is to use Sprague Atoms ,not expensive and they are the best replacement for this good amp .

https://www.tubesandmore.com/products/C-SA

Some of filter caps are low quality too.

For filter caps , use F & T caps

https://www.tubesandmore.com/products/C-ET22-500-FT

Replace the bias caps , close to pilot lamp, for a 100 MFD / 100 volts


+1

Mike,

Welcome to the forum.

The only thing I would add to stratele52's already excellent advice would be to replace the power cord with a 3 prong variety and get rid of the "death cap".

Thanks for posting pictures, it makes a huge difference as far as offering advice.

Merry Christmas!
vinyl


thanks vinyl, i've seen some of your posts so thanks for chiming in.
have a great 2015!

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please check out my Snakeskin's virtual music museum below.

http://muscmp.wordpress.com/


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Post subject: Re: 1965 blackface aa165
Posted: Thu Dec 25, 2014 6:21 pm
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so that i understand correctly:1. replace all 8 caps under the can/lid. 2. replace the 2 brown caps inside the chassis, one of which is a 25uf, 25 volt and the other is the one by the diodes, also 25uf 25 volt, that should be replaced with a 100uf, 100volt. 3. replace 2 prong with 3 prong cord. 4. cut death cap.

further questions, do i need to worry about the oxidization around the chassis ground solder? i read somewhere that you should clean it up. also, should i get some sort of a bias checker/setup? or use the bias pot and listen?
thanks again,
mikeB

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http://muscmp.wordpress.com/


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Post subject: Re: 1965 blackface aa165
Posted: Thu Dec 25, 2014 7:27 pm
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Mike,

Welcome to the Forum! This is an AB165 circuit. It has a balance pot bias circuit.

After all the cap changes, check the plate voltages on the 6L6GC's. Use a bias tool to find the idle bias current passing through those tubes. You cannot adjust this value using the balance or hum pot. If the bias is not in range (say around 18-20 watts per 6L6GC) --- you will need to play with the dropping resistor before the diode or the circuit-to-ground resistor on the balance pot --- to get the tubes into correct range.

You may want to consider changing the balance pot bias circuit to the AA165 --- bias pot circuit. With the AA165 circuit, you will have the ability to change the idle bias current. Check the two schematics to see the difference. If you decide to do this mod, post it. We can go further into how the mod is done. I've done several Fender amps -- from balance to bias mods.


AB165:

http://bmamps.com/Schematics/fender/bas ... _schem.pdf

AA165:

http://bmamps.com/Schematics/fender/bas ... _schem.pdf

-----

" Do I need to worry about the oxidization around the chassis ground solder? "


Don't worry about it. Unless you are having hum issues, after the caps are replaced. These discolorations are prolly dried solder flux and not surface rust.


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Post subject: Re: 1965 blackface aa165
Posted: Thu Dec 25, 2014 8:02 pm
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BMW2002Tii wrote:
Mike,

Welcome to the Forum! This is an AB165 circuit. It has a balance pot bias circuit.

After all the cap changes, check the plate voltages on the 6L6GC's. Use a bias tool to find the idle bias current passing through those tubes. You cannot adjust this value using the balance or hum pot. If the bias is not in range (say around 18-20 watts per 6L6GC) --- you will need to play with the dropping resistor before the diode or the circuit-to-ground resistor on the balance pot --- to get the tubes into correct range.

You may want to consider changing the balance pot bias circuit to the AA165 --- bias pot circuit. With the AA165 circuit, you will have the ability to change the idle bias current. Check the two schematics to see the difference. If you decide to do this mod, post it. We can go further into how the mod is done. I've done several Fender amps -- from balance to bias mods.


AB165:

http://bmamps.com/Schematics/fender/bas ... _schem.pdf

AA165:

http://bmamps.com/Schematics/fender/bas ... _schem.pdf

-----

" Do I need to worry about the oxidization around the chassis ground solder? "


Don't worry about it. Unless you are having hum issues, after the caps are replaced. These discolorations are prolly dried solder flux and not surface rust.

thanks, appreciate the information.
mikeB

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Post subject: Re: 1965 blackface aa165
Posted: Thu Dec 25, 2014 8:21 pm
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MikeB...I gotta ask, do you have more than one BF Bassman? One amp in another post was an AA165 I think, and this one is most assuredly a AB165 and the date stamps on the chassis are different. One is the 52 week of 64, and then this one is a is stamped OD on the Tube Chart and it of course a different Tube Chart. Did I miss something here?

T2

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Post subject: Re: 1965 blackface aa165
Posted: Thu Dec 25, 2014 8:42 pm
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T2Stratman wrote:
MikeB...I gotta ask, do you have more than one BF Bassman? One amp in another post was an AA165 I think, and this one is most assuredly a AB165 and the date stamps on the chassis are different. One is the 52 week of 64, and then this one is a is stamped OD on the Tube Chart and it of course a different Tube Chart. Did I miss something here?
T2


yes, you did. i have 2 posts. one for a blackface aa864 and one for an aa165. sorry i may have confused you. i'm trying to get both amps up to speed as i'll be selling one but figured i may as well do both and get them both ready.
thanks,
mikeB

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http://muscmp.wordpress.com/


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Post subject: Re: 1965 blackface aa165
Posted: Thu Dec 25, 2014 8:52 pm
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MikeB wrote:
T2Stratman wrote:
MikeB...I gotta ask, do you have more than one BF Bassman? One amp in another post was an AA165 I think, and this one is most assuredly a AB165 and the date stamps on the chassis are different. One is the 52 week of 64, and then this one is a is stamped OD on the Tube Chart and it of course a different Tube Chart. Did I miss something here?
T2


yes, you did. i have 2 posts. one for a blackface aa864 and one for an aa165. sorry i may have confused you. i'm trying to get both amps up to speed as i'll be selling one but figured i may as well do both and get them both ready.
thanks,
mikeB


Thanks for the clarification, I was beginning to think I had gone 'round the bend! The AA165 (from the other post) you have looks to be in the best condition internally at least. Of course condition is everything with vintage amps as you know so keep the best one since neither appear to be rarer than the other with the exception that the other posted amp is an FEIC vs a FMIC.

T2

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